The flow of heat in materials is generally perceived to be a slow process—in oxide glasses, heat diffuses a distance 1 mm on a time-scale of 1 sec—and therefore pump-probe techniques originally developed for ultrafast time-resolved optical spectroscopies are not an obvious source of technologies for advances in thermal property measurement. Nevertheless, over the past 15 years, the work of approximately 30 highly dedicated students and post- docs in Cahill's group at Illinois (together with many critical contributions from the groups of colleagues at several institutions in the US, Europe, and Asia) have developed time-domain thermoreflectance (TDTR) into a nearly universal, high-throughput tool for measuring the thermal conductivity of materials and the thermal conductance of materials interfaces. Cahill will illustrate the power of TDTR and open questions in the science of heat conduction in materials with recent examples drawn from: i) the thermal conductivity of high thermal conductivity crystals of BP, BAs, GaN, and SiC; ii) ultralow thermal conductivity in thin films of fullerene derivatives; iii) structure property relationships for thermal conductivity of amorphous polymers; and iv) thermal conductivity switching in liquid crystal networks and azopolymers.
David Cahill is the Willett Professor and Department Head of Materials Science and Engineering at the University of Illinois at Urbana-Champaign. He joined the faculty of the University of Illinois at Urbana-Champaign after earning his PhD in condensed matter physics from Cornell University, and working as a postdoctoral research associate at the IBM Watson Research Center. His research program focuses on developing a microscopic understanding of thermal transport at the nanoscale; the discovery of materials with enhanced thermal function; the interactions between phonons, electrons, photons, and spin; and advancing fundamental understanding of interfaces between materials and water. He received the 2015 Touloukian Award of the American Society of Mechanical Engineers and the Peter Mark Memorial Award from the American Vacuum Society (AVS); is a fellow of the AVS, American Physical Society (APS) and Materials Research Society (MRS); and a past-chair of the Division of Materials Physics of the APS.